Toners made by emulsion aggregation processes are useful in forming print and xerographic images. Emulsion aggregation processes typically involve the formation of a latex emulsion of polymer particles by heating a polymer in water, optionally with a solvent if needed, or by forming a latex emulsion of polymer particles using phase inversion emulsion (PIE). Additives such as emulsifying agents or surfactants, colorants, waxes, aggregating agents, and others may be included in the emulsion. The resulting latex particles may then be aggregated to form aggregated toner particles. Optionally, a second latex emulsion of polymer particles may be added to the aggregated toner particles, which upon further aggregation forms a shell on the aggregated toner particles. The resulting aggregated toner particles may be heated in a batch or continuous process to allow coalescence/fusing to occur, thereby providing aggregated, fused toner particles with increased circularity.
Various hybrid toner particles have been prepared. However, there remains a need for hybrid toner particles and methods for their preparation for use in toners for high speed printing, particularly high speed monochrome printing that provides excellent flow, charging, lower toner usage, and reduced drum contamination.
Emulsion aggregation toners may comprise various resins for use in forming the latex. One type of emulsion aggregation toner provides high gloss and uses styrene-acrylate, a lower costing resin. Another type of emulsion aggregation toner provides better fusing performance (e.g., lower Minimum Fusing Temperature (MFT) of about 20° C.) and uses polyesters as the base resin. However, the polyester resins used are high in cost. Thus, the present embodiments seek to form a hybrid emulsion aggregation toner that combines the advantages from both types of toners. However, it was discovered that toners with styrene-acrylate latexes do not melt at the same temperature during the toner process as the polyester toners, thus leading to variation in the surface morphology in a hybrid of the two toner types, as varying amounts of polystyrene/acrylate remains inhomogenously on the surface when the shell is initially predominately polyester. This issue is complicated by the fact that some styrene-acrylate migrates to the surface from the core. Thus, the present embodiments seek to avoid these issues by providing a core that comprises substantially polyester or, in the alternative, polyester and styrene-acrylate, and forming a shell comprising styrene-acrylate, with no polyester, over the core. This hybrid toner composition thus provides a lower costing toner that retains good fusing performance and low dielectric loss. Moreover, the shell improves the surface morphology by eliminating the variation in melting between the polyester and styrene-acrylate on the surface.